Commonly, it is desired to have the capability to change the speed of rotation of belt driven items on agricultural combines, such as crop residue choppers and the like. Typically to accomplish this, a tensioning mechanism for the belt or belts must be disengaged or released. The belt or belts must then be moved from one set of pulleys to a second set of pulleys. Then, the belt tension mechanism must be re-engaged. Belt tension on such drives is typically relatively high and thus a mechanical advantage device, such as a relatively long lever arm, is utilized to engage and disengage the tension mechanism. Moving the belt or belts can be difficult due to the length of the belts, and/or the location thereof.
Thus, what is sought is a belt drive shift mechanism for rotatable items on agricultural machines such as combines and the like, which eliminates the need for engaging and disengaging the belt tension mechanism, and physically moving the belt or belts from one set of pulleys to another.